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chemical element with symbol H and atomic number 1

Hydrogen is a chemical element. Its atomic number is 1, which makes it the lightest known element in the entire universe.[7] Hydrogen is the very oldest substance; the first kind of atom produced after the Big Bang. All chemical elements were formed from hydrogen by the processes of nuclear fusion.[8]

Hydrogen,  1H
Hydrogen discharge tube.jpg
Purple glow in its plasma state
General properties
Appearancecolorless gas
Standard atomic weight (Ar, standard)[1.007841.00811] conventional: 1.008
Hydrogen in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson


– ← hydrogenhelium
Atomic number (Z)1
Groupgroup 1
Periodperiod 1
Element category  reactive nonmetal
Electron configuration1s1
Electrons per shell
Physical properties
Phase at STPgas
Melting point13.99 K ​(−259.16 °C, ​−434.49 °F)
Boiling point20.271 K ​(−252.879 °C, ​−423.182 °F)
Density (at STP)0.08988 g/L
when liquid (at m.p.)0.07 g/cm3 (solid: 0.0763 g/cm3)[1]
when liquid (at b.p.)0.07099 g/cm3
Triple point13.8033 K, ​7.041 kPa
Critical point32.938 K, 1.2858 MPa
Heat of fusion(H2) 0.117 kJ/mol
Heat of vaporization(H2) 0.904 kJ/mol
Molar heat capacity(H2) 28.836 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 15 20
Atomic properties
Oxidation states−1, +1 (an amphoteric oxide)
ElectronegativityPauling scale: 2.20
Ionization energies
  • 1st: 1312.0 kJ/mol
Covalent radius31±5 pm
Van der Waals radius120 pm
Color lines in a spectral range
Spectral lines of hydrogen
Other properties
Natural occurrenceprimordial
Crystal structurehexagonal
Hexagonal crystal structure for hydrogen
Speed of sound1310 m/s (gas, 27 °C)
Thermal conductivity0.1805 W/(m·K)
Magnetic orderingdiamagnetic[2]
Magnetic susceptibility−3.98·10−6 cm3/mol (298 K)[3]
CAS Number12385-13-6
1333-74-0 (H2)
DiscoveryHenry Cavendish[4][5] (1766)
Named byAntoine Lavoisier[6] (1783)
Main isotopes of hydrogen
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
1H 99.98% stable
2H 0.02% stable
3H trace 12.32 y β 3He
| references


Hydrogen in natureEdit

In its pure form on Earth, hydrogen is usually a gas. Hydrogen is also one of the parts that make up a water molecule. Hydrogen is important because it is the fuel that powers the Sun and other stars. Hydrogen makes up about 74% of the entire universe.[9] Hydrogen's symbol on the Periodic Table of Elements is H.

Pure hydrogen is normally made of two hydrogen atoms connected together. Scientists call these diatomic molecules. Hydrogen will have a chemical reaction when mixed with most other elements. It has no color or smell.

Pure hydrogen is very uncommon in the Earth's atmosphere. In nature, it is usually in water. Hydrogen is also in all living things, as a part of the organic compounds that living things are made of. In addition, hydrogen atoms can combine with carbon atoms to form hydrocarbons. Petroleum and other fossil fuels are made of these hydrocarbons and commonly used to create energy for human use.

Hydrogen has two different isotopes, called deuterium and tritium. Like regular hydrogen, they both have only one proton and one electron, but deuterium also has one neutron and tritium has two. These other types of hydrogen are important in nuclear energy and organic chemistry reactions.

Some other facts about hydrogen:

History of HydrogenEdit

Hydrogen was first separated in 1671 by Robert Boyle. Henry Cavendish in 1776 identified it as a distinct element and discovered that burning it made water.

Antoine Lavoisier give Hydrogen its name, from the Greek word for water, 'υδορ (pronounced /HEEW-dor/) and gennen meaning to "generate" as it forms water in a chemical reaction with oxygen.

Uses of HydrogenEdit

The main uses are in the petroleum industry and in making ammonia by the Haber process. Some is used elsewhere in the chemical industry. A little of it is used as fuel, for example in rockets for spacecraft. Most of the hydrogen that people use comes from a chemical reaction between natural gas and steam.

Nuclear fusionEdit

Nuclear fusion is a very powerful source of energy. It relies on forcing atoms together to make helium and energy, exactly as happens in a star like the Sun, or in a hydrogen bomb. This needs a large amount of energy to get started, and is not easy to do yet. A big advantage over nuclear fission, which is used in today's nuclear power stations, is that it makes less nuclear waste and does not use a toxic and rare fuel like uranium. More than 600 million tons of hydrogen undergo fusion every second on the Sun.[11][12]

Burning HydrogenEdit

The electrolysis of water easily breaks water into hydrogen and oxygen, using electricity. Burning hydrogen combines with oxygen molecules to make steam (pure water vapor). A fuel cell combines hydrogen with an oxygen molecule, releasing an electron as electricity. For these reasons, many people believe hydrogen power will eventually replace other synthetic fuels.

Hydrogen can also be used as fuel in a fuel cell, or burned to make heat for steam turbines or internal combustion engines. Hydrogen can be created from many sources such as coal, natural gas or electricity, and therefore represents a valuable addition to the power grid; in the same role as natural gas. Such a grid and infrastructure with fuel cell vehicles is now planned by a number of countries including Japan, Korea and many European countries. This allows these countries to buy less petroleum, which is an economic advantage. The other advantage is that used in a fuel cell or burned in a combustion engine or turbine, there is no pollution. Only water, and a small amount of nitrogen oxides, forms.


  1. Wiberg, Egon; Wiberg, Nils; Holleman, Arnold Frederick (2001). Inorganic chemistry. Academic Press. p. 240. ISBN 978-0123526519.
  2. Lide, D. R., ed. (2005). "Magnetic susceptibility of the elements and inorganic compounds". CRC Handbook of Chemistry and Physics (PDF) (86th ed.). Boca Raton (FL): CRC Press. ISBN 978-0-8493-0486-6.
  3. Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 978-0-8493-0464-4.
  4. "Hydrogen". Van Nostrand's Encyclopedia of Chemistry. Wylie-Interscience. 2005. pp. 797–799. ISBN 978-0-471-61525-5.
  5. Emsley, John (2001). Nature's Building Blocks. Oxford: Oxford University Press. pp. 183–191. ISBN 978-0-19-850341-5.
  6. Stwertka, Albert (1996). A Guide to the Elements. Oxford University Press. pp. 16–21. ISBN 978-0-19-508083-4.
  7. 7.0 7.1 - What is Hydrogen?
  8. Carroll, Bradley W. & Ostlie, Dale A. 2006. An introduction to modern astrophysics. 2nd ed, Addison-Wesley, San Francisco. ISBN 0-8053-0402-9
  9. Cain, Fraser, Universe Today (November 7, 2016). "When was the first light in the universe?". Retrieved 29 November 2016.
  10. "The magic of syngas". 2012. Retrieved 7 March 2012.
  11. "What is Fusion?". ITER Organization. 2012. Retrieved 7 March 2012.
  12. "NASA's Cosmicopia". NASA. Retrieved 28 February 2013.

Other websitesEdit